Before you delete your old documents, please consider the followings:

1. The value of keeping them is that their stats count towards your rankings within the edocr ecosystem against other companies. 
2. If you decide your rankings does not matter, you can delete them, but make sure you extracted the leads (who read the document) first. 
3. If you think ranking does matter, or content is still relevant, you can keep them, e.g. user manual of a product you no longer sells will still be of high demand by the current users of that product. 
4. You could also replace them with a new document and change the title and description. This way you retain the stats.